This invention relates to nuclear reactor fuel elements.
It has been proposed that nuclear reactor fuel elements of the kind in which nuclear fuel material is enclosed in a protective sheath should be individually identifiable by providing within each sheath an insert which is unique to that fuel element. Such inserts may conveniently be provided with markings whereby a digital output train of pulses can be produced, on passage of the fuel element through an activated eddy current head, for example, and de-coding equipment can readily be devised to accept these sequential pulses. However this is a time dependent function and if the position of the markings is to be correctly identified it is essential to control strictly the relative movement of insert and marking detector. This may be difficult.